From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.bootlin.com ([62.4.15.54]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1fmKPC-0005UD-R7 for linux-mtd@lists.infradead.org; Sun, 05 Aug 2018 14:53:18 +0000 From: Miquel Raynal To: Boris Brezillon , Richard Weinberger , David Woodhouse , Brian Norris , Marek Vasut Cc: linux-mtd@lists.infradead.org, Miquel Raynal Subject: [PATCH v4 1/2] mtd: rawnand: marvell: document a bit more the driver Date: Sun, 5 Aug 2018 16:52:56 +0200 Message-Id: <20180805145257.15256-1-miquel.raynal@bootlin.com> List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , A stale document about the old pxa3cc_nand.c driver is available in Documentation/mtd/nand/. Rewrite the parts that explain the IP itself and some non-trivial choices made in the driver directly in marvell_nand.c to then be able to remove this file. Signed-off-by: Miquel Raynal --- Changes since v2: ================= * Addressed Boris comments, fixed (new) typos, explained what spare bytes and naked operations are. Changes since v2: ================= * Addressed Boris comments, mostly typos and rewritting as suggested. Changes since v1: ================= * Corrected mistakes pointed by Boris. * Enlarged the documentation as suggested by Thomas to mention the layouts as seen per the controller. * Added a mention about the maximum ECC size which is 2kiB. drivers/mtd/nand/raw/marvell_nand.c | 67 +++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) diff --git a/drivers/mtd/nand/raw/marvell_nand.c b/drivers/mtd/nand/raw/marvell_nand.c index 218e09431d3d..53ebd5cb3e6e 100644 --- a/drivers/mtd/nand/raw/marvell_nand.c +++ b/drivers/mtd/nand/raw/marvell_nand.c @@ -5,6 +5,73 @@ * Copyright (C) 2017 Marvell * Author: Miquel RAYNAL * + * + * This NAND controller driver handles two versions of the hardware, + * one is called NFCv1 and is available on PXA SoCs and the other is + * called NFCv2 and is available on Armada SoCs. + * + * The main visible difference is that NFCv1 only has Hamming ECC + * capabilities, while NFCv2 also embeds a BCH ECC engine. Also, DMA + * is not used with NFCv2. + * + * The ECC layouts are depicted in details in Marvell AN-379, but here + * is a brief description. + * + * When using Hamming, the data is split in 512B chunks (either 1, 2 + * or 4) and each chunk will have its own ECC "digest" of 6B at the + * beginning of the OOB area and eventually the remaining free OOB + * bytes (also called "spare" bytes in the driver). This engine + * corrects up to 1 bit per chunk and detects reliably an error if + * there are at most 2 bitflips. Here is the page layout used by the + * controller when Hamming is chosen: + * + * +-------------------------------------------------------------+ + * | Data 1 | ... | Data N | ECC 1 | ... | ECCN | Free OOB bytes | + * +-------------------------------------------------------------+ + * + * When using the BCH engine, there are N identical (data + free OOB + + * ECC) sections and potentially an extra one to deal with + * configurations where the chosen (data + free OOB + ECC) sizes do + * not align with the page (data + OOB) size. ECC bytes are always + * 30B per ECC chunk. Here is the page layout used by the controller + * when BCH is chosen: + * + * +----------------------------------------- + * | Data 1 | Free OOB bytes 1 | ECC 1 | ... + * +----------------------------------------- + * + * ------------------------------------------- + * ... | Data N | Free OOB bytes N | ECC N | + * ------------------------------------------- + * + * --------------------------------------------+ + * Last Data | Last Free OOB bytes | Last ECC | + * --------------------------------------------+ + * + * In both cases, the layout seen by the user is always: all data + * first, then all free OOB bytes and finally all ECC bytes. With BCH, + * ECC bytes are 30B long and are padded with 0xFF to align on 32 + * bytes. + * + * The controller has certain limitations that are handled by the + * driver: + * - It can only read 2k at a time. To overcome this limitation, the + * driver issues data cycles on the bus, without issuing new + * CMD + ADDR cycles. The Marvell term is "naked" operations. + * - The ECC strength in BCH mode cannot be tuned. It is fixed 16 + * bits. What can be tuned is the ECC block size as long as it + * stays between 512B and 2kiB. It's usually chosen based on the + * chip ECC requirements. For instance, using 2kiB ECC chunks + * provides 4b/512B correctability. + * - The controller will always treat data bytes, free OOB bytes + * and ECC bytes in that order, no matter what the real layout is + * (which is usually all data then all OOB bytes). The + * marvell_nfc_layouts array below contains the currently + * supported layouts. + * - Because of these weird layouts, the Bad Block Markers can be + * located in data section. In this case, the NAND_BBT_NO_OOB_BBM + * option must be set to prevent scanning/writing bad block + * markers. */ #include -- 2.14.1